The present invention relates of a load drive apparatus used to drive a motor, a solenoid or the like.
In a recent automatic control system for vehicles, a load control circuit uses a semiconductor switching device for driving electric loads. However, as the load consumes more electric power, the semiconductor switching device becomes larger in size, resulting in that the manufacturing yield is lowered, package quality is also lowered and manufacturing cost rises.
It is proposed to use a plurality of semiconductor switching devices connected in parallel for driving the load, thereby to reduce the power supplied to each semiconductor switching device. In addition, it is also proposed to protect each semiconductor switching device from excessive heating due to short-circuit of the load, and from over voltage and low voltage failure due to a failure of an alternator or a battery.
However, each semiconductor switching device does not turn off simultaneously, but turns off keeping a certain time difference due to variation of detection level in each device during the parallel drive. Thus, a load current concentrates on the switching device that is delayed to turn off even if each semiconductor switching device is caused to turn off during detection of an abnormality.
It is an object of the present invention to provide a load drive device which prevents the power from concentrating in any semiconductor switching device.
According to the present invention, a plurality of switching circuits having respective switching devices are respectively provided with INH input terminals and INH output terminals. The INH input terminals are connected to the INH output terminals. When a signal to turn off the switching devices is outputted from any INH output terminal of the switching circuits, this signal is inputted to the INH input terminals of the other switching circuits. Thus, all the switching circuits turn off the respective switching devices simultaneously. Thereby, at the time of parallel drive of the semiconductor switching devices for driving an electric load, it can be prevented that the power concentrates on any semiconductor switching device due to variation in switching operations.